Gas separation devices have been used in incinerators, air conditioners, diesel engines, and the like. The gas separation device can generate a nitrogen-enriched gas or an oxygen-enriched gas by allowing oxygen in the air including oxygen and nitrogen to pass through a membrane element. In addition, in the gas separation device, humidification or dehumidification of gas can be performed by allowing water vapor to pass through the membrane element.
The gas separation device in a combustion furnace can be used to suppress production of dioxin and to increase combustion efficiency. Specifically, oxygen in the air may be passed through a gas separation membrane to generate the oxygen-enriched air, which is introduced to the combustion furnace to increase the combustion temperature, thereby suppressing production of dioxin. By using the oxygen-enriched air, even a low-calorie fuel can be burnt at a prescribed temperature.
In addition, the gas separation device can be used to suppress nitrogen oxide by introducing the nitrogen-enriched air into a combustion furnace. The nitrogen-enriched air can be generated by allowing oxygen in the air to pass through a gas separation membrane to remove oxygen.
The gas separation device in an air conditioner has been used to separate the air into oxygen and nitrogen and to introduce the oxygen-enriched air into a room. It has also been used in humidification or dehumidification by allowing water vapor to pass through the membrane.
In internal combustion engines widely used in automobile engines, when the combustion temperature becomes high, nitrogen reacts with oxygen to produce nitrogen oxide (NOx), which is exhausted. In the case of gasoline engines, a three-way catalyst serves as a system for removing nitrogen oxide (NOx). This three-way catalyst can remove hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) in the exhaust gas simultaneously through an oxidation-reduction reaction.
However, in diesel engines in which a fuel is burnt with excessive air, the three-way catalyst does not function effectively since oxygen is included in the exhaust gas. Therefore, in the case of diesel engines, a method of decreasing an oxygen concentration in the air supplied to a combustion chamber to reduce the combustion temperature is an example of one of effective methods. As a specific example thereof, an EGR system (Exhaust Gas Recirculation system) is a method of reducing an oxygen concentration in the supply air by recirculating and mixing part of exhaust gas into the air.
Another example is a method of reducing nitrogen oxide (NOx) by supplying the nitrogen-enriched air to a combustion chamber using a gas separation device. A method of reducing a combustion temperature by supplying the humidified air to a combustion chamber is also effective. The gas separation device can also be used as a device for generating the nitrogen-enriched air with a low oxygen concentration, or the humidified air.
In the gas separation devices used in various applications as described above, a variety of studies have been done so far in order to improve the ability of separating gas (gas separation performance). For example, Patent Literature 1 discloses a flat pleat-type membrane element and a gas separator using the membrane element. The membrane element described in Patent Literature 1 has a configuration in which a reinforcement frame is arranged on the outer periphery of a pleat molding formed by pleating a gas separation membrane. In the gas separator having this membrane element, a plate having an intake port and an exhaust port is used as a housing that accommodates the membrane element.
Patent Literature 2 discloses a gas separator configured to include two membrane elements with top surfaces thereof arranged to face each other, a pair of pressure plates sandwiching the two membrane elements from the bottom surface sides, a pipe for supplying or exhausting a gas mixture to the primary side of the top surface of the membrane element, and a secondary-side channel for discharging the air passing through the membrane element and being exhausted from the bottom surface side. In this gas separator, the pipe and the like for supplying the gas mixture are arranged on the left and right of the two membrane elements arranged above and below. The gas mixture flowing through the supply-side pipe passes through a slit-like narrow path to be supplied to the primary-side channel of the membrane element and further passes through a slit-like narrow path to be discharged to the exhaust-side pipe.